Project Summary Increased intestinal permeability plays a crucial role in a number of chronic intestinal inflammatory conditions including Type 1 Diabetes (T1D), celiac disease, as well as Crohn?s disease (CD) and ulcerative colitis (UC), collectively referred to as inflammatory bowel disease (IBD). More than 1.4 million Americans suffer from IBD. While the exact cause(s) of IBD are unknown, there is considerable evidence that a permeability defect in the intestinal epithelial cell (IEC) layer plays a major role in the development of IBD. The intestinal epithelial lining is a single layer of cells that forms the interface between the bacteria that reside in the intestine (intestinal microbiota), and the rest of the body. During inflammation, the epithelium is exposed to high levels of inflammatory mediators such as interferon-? (IFN?). These mediators activate signaling pathways that alter various functions of the epithelium, such as barrier maintenance. Termination of these signals is mediated largely by the activity of phosphatases. One such phosphatase, protein tyrosine phosphatase non-receptor type 2 (PTPN2), negatively regulates IFN? signaling in non-epithelial cells. However, little is known about the function of PTPN2 in the intestinal epithelium. Single nucleotide polymorphisms (SNP) in the PTPN2 gene have been confirmed as a genetic marker associated with Crohn?s disease, UC, T1D and celiac disease. Thus, these diseases share a common gene association and an elevation in intestinal permeability. We have identified a completely novel involvement of PTPN2 in the regulation of epithelial barrier function. Therefore, the specific objectives of this proposal are to better understand how PTPN2 loss-of-function mutations alter phosphorylation signaling networks impacting upon intestinal barrier function, and if this can be corrected by a clinically-effective therapeutic agent. This will be addressed in three specific aims. Aim 1: Determine the molecular mechanisms causing epithelial barrier defects due to PTPN2 loss of function Aim 2: PTPN2 is a negative regulator of JAK-STAT inflammatory signaling pathways. We will investigate if the JAK inhibitor, Tofacitinib can correct the consequences of PTPN2 loss of function through inhibiting JAK-STAT pathways normally restricted by PTPN2. Aim 3: Identify how loss of PTPN2 phosphatase activity alters its ?phospho- interactome? in IEC and how does this impact upon tight junction protein phosphoregulation. Expected Outcomes & Impact: These studies will not only build a more accurate mechanistic understanding of the consequences of loss-of-function PTPN2 mutations for barrier function regulation and associated signaling networks, but will also identify a possible therapeutic approach to resolve these defects.